1. Field of the Invention
The present invention relates generally to cement set retarding additives, hydraulic: cement compositions including the additives and methods of using the set retarded compositions for cementing subterranean zones in wells.
2. Description of the Prior Art
A variety of procedures involving hydraulic cement compositions are utilized in the construction and repair of wells such as oil, gas and water wells. For example, in the completion of a well after a well bore has been drilled into one or more subterranean producing formations, a pipe such as casing is disposed in the well bore and a hydraulic cement composition is pumped into the annular space between the walls of the well bore and the exterior of the pipe. The cement composition is allowed to set in the annular space whereby an annular cement sheath is formed therein which bonds the pipe to the walls of the well bore and prevents the undesirable flow of fluids into and through the annular space.
In repairing producing wells, hydraulic cement compositions are often utilized to plug holes or cracks in the pipe disposed in the well bore; to plug holes, cracks, voids or channels in the aforementioned cement sheath between the pipe and the well bore; to plug permeable zones or fractures in subterranean formations and the like. The holes, cracks, etc. are repaired by forcing hydraulic cement compositions thereinto which harden and form impermeable plugs therein.
High temperatures are frequently encountered in deep subterranean zones to be cemented. The combination of the depth of the zone and the high temperature thereof often results in the requirement that the setting time of the cement composition be extended to allow the cement composition to be pumped into the zone to be cemented. Set retarding additives have been developed and used for this purpose, and such additives have been mixed with well cement compositions in amounts sufficient to delay the setting of the compositions until they can be pumped into desired subterranean locations.
While a variety of set retarding additives have been developed and used successfully heretofore, they can and often do produce erratic results in cement compositions of different component make-up and/or cause premature gelation of cement compositions when they are subjected to the high temperature environments of deep subterranean zones. The high temperatures referred to herein are temperatures of 200.degree. F. and higher, and the gelation referred to is the abnormal increase in viscosity of a cement composition without an increase in compressive strength. The increase in viscosity makes the cement composition difficult or impossible to pump even though the cement composition has not set. In addition, a number of the prior art set retarding additives are comprised of materials which are expensive to produce. Thus, there is a continuing need for improved cement set retarding additives which do not cause premature gelation and which are relatively inexpensive, set retarded hydraulic cement compositions containing the additives and methods of using the compositions for carrying out cementing operations in wells.